This invention concerns a process for treating slop oil. More particularly, the invention concerns a method of treating slop oil in an electric coalescer apparatus. The invention also concerns a method for operating an electric coalescer that has interface problems. The utility of the invention resides in the reclamation and re-use of oily wastes, such as are found in a petroleum refinery.
Slop oil treatment is most typically found in a petroleum refinery, but the present invention can also be applied in the treatment of used railroad oil or in the recovery of cutting oils used in a steel plant. One way of treating such oily wastes is by gravity separation, wherein the oil-water mixture or emulsion is fed to a container, the oily and watery phases are allowed to separate, and the separated layers are removed. Since this method frequently requires a relatively long time and many containers having large volumes, electric coalescers are frequently used. A typical procedure is to add the slop oil-water mixture to the coalescer, along with emulsion-breaking chemicals. Under the influence of the direct current electric field in the coalescer, the emulsion breaks, giving an oily top layer and an aqueous bottom layer. The main source of trouble in a coalescer is the interface emulsion between the layers of oil and water, the most difficult portion of the mixture to treat.
If this interface emulsion level rises in the coalescer until it touches the coalescer plates, the interface, being conductive, tends to arc and short out the electrical system. Also, the emulsion through which the arc passes tends to separate, with the oily portion attaching itself to the coalescer plates. This results in a contaminating, non-conducting layer on the coalescer plates, necessitating a shutdown and cleaning of the coalescer.
In typical, prior art coalescers, this interface level was non-detectable and needed to be kept away from the coalescer plates.